With an increased demand for strong privacy protection, a variety of related products have been developed in different fields. Among the privacy-preserving products, privacy filters that fit over a mobile phone or computer screen to block the lateral transmission and narrow the screen's viewing angle have been in increasing demand every year. Unfortunately, the viewing angle, once narrowed, is not restorable without eliminating the privacy filter from the screen, incurring inconvenience that the privacy filter has to be removed from the screen whenever the privacy protection function is not needed.
To remove the inconvenience, there has recently been developed a switchable privacy filter that does not involve add-on films but controls the viewing angle selectively according to the reception of electrical signals. Blocking the light for the switchable privacy filters can be achieved in different ways, such as using PDLC (Polymer Dispersed Liquid Crystal) or PNLC (Polymer Network Liquid Crystal) as a light-absorbing material; employing a separate LCD structure; or applying an electrochromic material. However, the common disadvantages of the switchable privacy filters realized by those different methods are poor lateral transmission in the privacy mode, extremely low front transmission, slow switching between wide field mode and narrow field mode, deteriorated performance and driving stability in continuous mode switching, and so forth. Sustainable studies have been made in searching for a solution to those problems, still no apparent development of privacy filters that fit the needs.